refactor(selector): share IsFailed dead-node check with FailFilter

Extract the per-item failed-state decision (failure count >= maxFails,
last failure within failTimeout, metadata overrides) from FailFilter
into an exported IsFailed helper, and reuse it in the hop's
pre-selection dead-node filter instead of a local duplicate.

hop/hop.go

@@ -270,7 +270,7 @@ func (p *chainHop) Select(ctx context.Context, opts ...hop.SelectOption) *chain.
 	if len(nodes) > 0 {
 		alive := nodes[:0]
 		for _, n := range nodes {
-			if !nodeIsFailed(n, p.options.failMaxFails, p.options.failTimeout) {
+			if !xs.IsFailed(n, p.options.failMaxFails, p.options.failTimeout) {
 				alive = append(alive, n)
 			}
 		}
@@ -368,24 +368,6 @@ func isAllBackup(nodes []*chain.Node) bool {
 	return len(nodes) > 0
 }
 
-// nodeIsFailed reports whether node is currently marked failed per the same
-// criteria FailFilter uses: failure count has reached maxFails and the last
-// failure is still within failTimeout. FailFilter itself no-ops on a single
-// node, so the priority short-circuit checks the marker directly here.
-func nodeIsFailed(node *chain.Node, maxFails int, timeout time.Duration) bool {
-	marker := node.Marker()
-	if marker == nil {
-		return false
-	}
-	if maxFails <= 0 {
-		maxFails = xs.DefaultMaxFails
-	}
-	if timeout <= 0 {
-		timeout = xs.DefaultFailTimeout
-	}
-	return !(marker.Count() < int64(maxFails) || time.Since(marker.Time()) >= timeout)
-}
-
 func (p *chainHop) isEligible(node *chain.Node, opts *hop.SelectOptions) bool {
 	if node == nil {
 		return false

selector/filter.go

@@ -30,39 +30,50 @@ func (f *failFilter[T]) Filter(ctx context.Context, vs ...T) []T {
 	}
 	var l []T
 	for _, v := range vs {
-		maxFails := f.maxFails
-		failTimeout := f.failTimeout
-		if mi, _ := any(v).(metadata.Metadatable); mi != nil {
-			if md := mi.Metadata(); md != nil {
-				if md.IsExists(labelMaxFails) {
-					maxFails = mdutil.GetInt(md, labelMaxFails)
-				}
-				if md.IsExists(labelFailTimeout) {
-					failTimeout = mdutil.GetDuration(md, labelFailTimeout)
-				}
-			}
+		if !IsFailed(v, f.maxFails, f.failTimeout) {
+			l = append(l, v)
 		}
-		if maxFails <= 0 {
-			maxFails = 1
-		}
-		if failTimeout <= 0 {
-			failTimeout = DefaultFailTimeout
-		}
-
-		if mi, _ := any(v).(selector.Markable); mi != nil {
-			if marker := mi.Marker(); marker != nil {
-				if marker.Count() < int64(maxFails) ||
-					time.Since(marker.Time()) >= failTimeout {
-					l = append(l, v)
-				}
-				continue
-			}
-		}
-		l = append(l, v)
 	}
 	return l
 }
 
+// IsFailed reports whether v is currently marked failed: its failure count
+// has reached maxFails and the last failure is still within failTimeout.
+// Per-item metadata keys "maxFails" and "failTimeout" override the given
+// defaults. Items without a failure marker are never considered failed.
+func IsFailed[T any](v T, maxFails int, failTimeout time.Duration) bool {
+	maxFails, failTimeout = effectiveFailSettings(v, maxFails, failTimeout)
+
+	mi, _ := any(v).(selector.Markable)
+	if mi == nil || mi.Marker() == nil {
+		return false
+	}
+	marker := mi.Marker()
+	return !(marker.Count() < int64(maxFails) || time.Since(marker.Time()) >= failTimeout)
+}
+
+// effectiveFailSettings resolves the maxFails/failTimeout for v, honoring
+// per-item metadata overrides and defaulting to 1 / DefaultFailTimeout.
+func effectiveFailSettings[T any](v T, maxFails int, failTimeout time.Duration) (int, time.Duration) {
+	if mi, _ := any(v).(metadata.Metadatable); mi != nil {
+		if md := mi.Metadata(); md != nil {
+			if md.IsExists(labelMaxFails) {
+				maxFails = mdutil.GetInt(md, labelMaxFails)
+			}
+			if md.IsExists(labelFailTimeout) {
+				failTimeout = mdutil.GetDuration(md, labelFailTimeout)
+			}
+		}
+	}
+	if maxFails <= 0 {
+		maxFails = 1
+	}
+	if failTimeout <= 0 {
+		failTimeout = DefaultFailTimeout
+	}
+	return maxFails, failTimeout
+}
+
 type backupFilter[T any] struct{}
 
 // BackupFilter filters the backup objects.

selector/filter_test.go

@@ -264,3 +264,33 @@ func TestFilterMetadataLabels(t *testing.T) {
 		t.Fatalf("failTimeout: expected 30s, got %v", ft)
 	}
 }
+
+// --- IsFailed shared helper tests ---
+
+func TestIsFailed(t *testing.T) {
+	item := newTestMarkable(nil)
+
+	if IsFailed(item, 1, 10*time.Second) {
+		t.Fatal("unmarked item should not be failed")
+	}
+
+	item.Marker().Mark()
+	if !IsFailed(item, 1, 10*time.Second) {
+		t.Fatal("marked item with maxFails=1 should be failed")
+	}
+	if IsFailed(item, 2, 10*time.Second) {
+		t.Fatal("single mark below maxFails=2 should not be failed")
+	}
+
+	// Per-item metadata override beats the given defaults.
+	item2 := newTestMarkable(map[string]any{"maxFails": 1, "failTimeout": "60s"})
+	item2.Marker().Mark()
+	if !IsFailed(item2, 5, 10*time.Second) {
+		t.Fatal("metadata maxFails override should take precedence")
+	}
+
+	// Non-markable items are never failed.
+	if IsFailed(42, 1, time.Second) {
+		t.Fatal("non-markable item should not be failed")
+	}
+}